1. Field of the Invention
The present invention relates to a method of driving a plasma display panel (hereinafter, also referred to as xe2x80x9cPDPxe2x80x9d).
2. Description of the Background Art
Various studies have been made on a PDP as a thin-type television and a display monitor. Among the PDPs, there is a surface discharge AC-type PDP as one of AC-type PDPs having a memory function.
(Structure of PDP)
FIG. 28 is a perspective view showing an AC-type PDP 101 in the background art. The PDP of this structure is disclosed in Japanese Patent Application Laid Open Gazette Nos. 7-140922 and 7-287548.
The PDP 101 comprises a front glass substrate 102 as a display surface and a rear glass substrate 103 opposed to the front glass substrate 102 with a discharge space sandwiched therebetween.
On a surface of the front glass substrate 102 on the side of the discharge space 111, n sip-like electrodes 104a and n strip-like electrodes 105a which are paired respectively are extendedly formed. For convenience of illustration range, one electrode 104a and one electrode 105a are shown in FIG. 28. The electrodes 104a and 105a which are paired with each other are arranged with a discharge gap DG interposed therebetween. The electrodes 104a and 105a work to induce a discharge. Further, a transparent electrode is used for the electrodes 104a and 105a to extract more visible light, and hereinafter the electrodes 104a and 105a are also referred to as transparent electrodes 104a and 105a. Furthermore, in some cases, the electrodes 104a and 105a are made of the same material as metal (auxiliary) electrodes (or bus electrodes) 104b and 105b as discussed later are made of. On the transparent electrodes 104a and 105a, the metal (auxiliary) electrodes (or bus electrodes) 104b and 105b are formed extendedly along the transparent electrodes 104a and 105a. The metal electrodes 104b and 105b have impedance lower than those of the transparent electrodes 104a and 105a, and work to supply a current from a driving device.
In the following discussion, an electrode constituted of the transparent electrode 104a and the metal electrode 104b is referred to as a (row) electrode 104 (or X) and an electrode constituted of the transparent electrode 105a and the metal electrode 105b is referred to as a (row) electrode 105 (or Y). The row electrodes 104 and 105 (or row electrodes X and Y) which are paired with each other are also referred to as a pair of (row) electrodes 104 and 105 (or a pair of (row) electrodes X and Y). Further, in some cases, the row electrode 104 is constituted of only an electrode which corresponds to the electrode 104a, and/or the row electrode 105 is constituted of only an electrode which corresponds to the electrode 105a. 
A dielectric layer 106 is formed covering the row electrodes 104 and 105 and a protection film 107 made of MgO (magnesium oxide) which is a dielectric substance is formed on a surface of the dielectric layer 106 by evaporation method and the like. The dielectric layer 106 and the protection film 107 are also generally referred to as a dielectric layer 106A. Further, in some cases, the dielectric layer 106A does not include the protection film 107.
On the other hand, on a surface of the rear glass substrate 103 on the side of the discharge space 111, m strip-like (column) electrodes 108 are so formed extendedly as to be orthogonal to (as to grade-separately intersect) the row electrodes 104 and 105. Hereinafter, the (column) electrode 108 is also referred to as a (column) electrode W. Furthermore, for convenience of illustration range, three electrodes 108 are shown in FIG. 28.
Between the adjacent column electrodes 108, a barrier rib 110 is formed extendedly in parallel with the column electrodes 108. The barrier ribs 110 separate a plurality of discharge cells (discussed later) arranged along the extending direction of the row electrodes 104 and 105 from each other and the barrier ribs 110 support the PDP 101 so as not to be crushed by atmospheric pressure.
Inside a substantial U-shaped trench constituted of the adjacent barrier ribs 110 and the rear glass substrate 103, a phosphor layer 109 is formed covering the column electrode 108. In more detail, in the above substantial U-shaped trenches, phosphor layers 109R, 109G and 109B for respective emitted light colors, red, green and blue are formed and for example, the phosphor layers 109R, 109G and 109B are arranged in this order in the entire PDP 101.
The front glass substrate 102 and the rear glass substrate 103 having the above structure are sealed with each other and the discharge space 111 between the front glass substrate 102 and the rear glass substrate 103 is filled with discharge gas such as Nexe2x80x94Xe mixed gas or the Hexe2x80x94Xe mixed gas under a pressure lower than the atmospheric pressure.
In the PDP 101, a discharge cell or a light emitting cell is formed at a (grade-separation) intersection of the row electrodes 104 and 105 and the column electrode 108. Specifically, three discharge cells are shown in FIG. 28.
(Principle of Operation of PDP)
Next, a principle of display operation of the PDP 101 will be discussed. First, a voltage or a voltage pulse is applied across the row electrodes 104 and 105 to generate a discharge in the discharge space 111. Then, by exciting the phosphor layer 109 with an ultraviolet ray generated by this discharge, the discharge cell emits light or lights up.
Charged particles such as electrons and ions generated in the discharge space 111 through this discharge move in a direction of the row electrode to which a voltage having a polarity reverse to that of the charged particles is applied and are accumulated on the surface of the dielectric layer 106A on the row electrode (referred to as xe2x80x9con the row electrodexe2x80x9d hereinafter). The electric charges such as electrons and ions accumulated on the surface of the dielectric layer 106A are referred to as xe2x80x9cwall charges.xe2x80x9d
Since the respective wall charges accumulated on the row electrodes 104 and 105 through the discharge form an electric field in a direction of weakening the electric field between the pair of the row electrodes 104 and 105, the discharge quickly disappears with formation and accumulation of the wall charges. When a voltage having polarity reverse to that of the above voltage is applied to the row electrodes 104 and 105 after the discharge disappears, an electric field in which the electric field generated by the applied voltage is superimposed on the electric field generated by the wall charges is substantially applied to the discharge space 111, in other words, a voltage in which the applied voltage is superimposed on the voltage (wall voltage) generated by the wall charges is substantially applied to the discharge space 111. The superimposed electric field can cause a discharge again.
Specifically, once the discharge is generated, continuous discharge (sustain discharge) can be caused by a voltage (sustain voltage) lower than the applied voltage used for starting the initial discharge through the electric field generated by the wall charges. Therefore, after the discharge is once generated, by alternately applying a pulse (sustain pulse) having an amplitude of sustain voltage to the row electrodes 104 and 105, in other words, by applying the sustain pulse across the row electrodes 104 and 105 with its polarity reversed, the discharge can be regularly sustained and continued (sustain operation).
Specifically, the discharge can be continued by continuously applying the sustain pulse until the wall charges disappear. Further, to extinguish the wall charges is referred to as xe2x80x9can erase operationxe2x80x9d (or simply as xe2x80x9can erasexe2x80x9d) while to form the wall charges on the dielectric layer 106A at the start of continuous discharge (sustain discharge) is referred to as xe2x80x9ca writing operationxe2x80x9d (or simply as xe2x80x9ca writingxe2x80x9d).
An actual image display is repeated with one field set within 16.6 ms, considering the human visual characteristics. At this time, in general, one field is divided into a plurality of subfields and the subfields have different luminances to make a gradation or tone. One subfield includes a reset period, an addressing period and a sustain period.
In the reset period, discharge (priming discharge) is generated in all the cells regardless of display history in order to enhance the discharge probability. Concurrently with this discharge, the wall charges are erased to erase the display history.
In the addressing period, a discharge cell is selected in matrix by combination of the row electrode 104 (105) and the column electrode 108 to generate a discharge (writing discharge or addressing discharge) in the predetermined discharge cell(s).
In the sustain period, discharges are repeatedly generated a predetermined number of times in the discharge cell(s) in which the writing discharge is generated in the addressing period. The luminance depends on the number of repeating generations of discharges.
In a predetermined discharge cell (or a plurality of predetermined discharge cells) among a plurality of discharge cells arranged in matrix, the writing discharge is first generated and then the sustain discharge is generated, to display characters, figures, images and the like. Further, by quickly performing the writing operation, the sustain operation and the erase operation, a movie display can be also performed. In this case, the number of tones can be increased by reducing the respective times of writing operation, sustain operation and erase operation. On the other hand, in a case of the same number of tones, a stable driving voltage margin can be obtained by increasing the respective operation times.
(Driving Method Using Round Pulse)
In general, as a sustain pulse used is a rectangular waveform or a rectangular pulse having a sharp rise, in other words, a rectangular pulse which rises fast. The rectangular pulse is used in order to generate an intense discharge by the sustain pulse and thereby generate a sufficient amount of wall charges. In more detail, in a case of using the rectangular pulse which rises sufficiently fast, the discharge starts after the rectangular pulse reaches a final attainment potential (or final attainment voltage; hereinafter, also referred to simply as a final potential (or final voltage)). Specifically, from the time when the applied voltage exceeds a firing voltage until the discharge is actually generated, there is a time lag called a discharge delay time. The applied rectangular pulse reaches the final potential before the discharge delay time passes. Therefore, since a sufficient high voltage is applied to the discharge space, a lot of wall charges are generated and accumulated.
In contrast to this, as the priming discharge and the like, a pulse of round waveform, i.e., a round pulse is used, in some cases. Since it is desirable that a discharge not for display luminescence, such as the priming discharge, is weak in terms of contrast, the round pulse which can generate a relatively weak discharge is used. Further, also when the wall charges are erased, a predetermined amount of wall charges are generated or the like, the round pulse is sometimes used.
When the rise time (and/or fall time) of the round pulse is longer than the discharge delay time and the round pulse rises (falls) sufficiently slow, a very weak discharge starts at the minimum voltage value. In the case of this discharge, the amount of movement of wall charges is very small and the discharge continues all the while the voltage continues to change after the discharge starts. In more detail, the discharge is once generated near the firing voltage to generate a very small amount of wall charges. Since the voltage across electrodes exceeds the firing voltage again with the continuous rise of the applied voltage, the discharge is generated again. By repeating generations of such a very small discharge, a weak discharge continues all the while the applied voltage continues to change. At this time, a predetermined amount of wall charges which depend on the final potential of the round pulse are stably generated. Furthermore, it is possible to extinguish the wall charges, depending on the application polarity and the final potential of the round pulse.
The round pulse mainly includes two types of pulses, i.e., a xe2x80x9cCR waveform (or CR pulse)xe2x80x9d and a xe2x80x9cramp waveform (or ramp pulse)xe2x80x9d. These waveforms will be discussed below.
The CR pulse is obtained when a capacitance element is charged (or discharged) through a resistance element. When a capacitance element C having a voltage of 0 in an initial state is charged by a power supply having a voltage V0( greater than 0) through a resistance element R, a voltage of the capacitance element C, i.e., a voltage v(t) of the CR pulse is expressed as
v(t)=V0xc3x97(1xe2x88x92exp (xe2x88x92t/xcfx84)) 
where t represents time and xcfx84 is a time constant expressed by a product of the capacitance element C and the resistance element R (xcfx84=Cxc3x97R). Since the voltage v(t) includes a term of exponential function, the waveform of the voltage v(t) is sometimes termed xe2x80x9can exponential waveformxe2x80x9d.
The rate of change dv(t)/dt (hereinafter, also referred to as xe2x80x9cdv/dtxe2x80x9d) of the voltage v(t) with respect to time t is obtained as
dv(t)/dt=(V0/xcfx84)xc3x97exp(xe2x88x92t/xcfx84) 
It can be seen from this equation that the rate of voltage change dv(t)/dt of the CR pulse is large immediately after the application and gradually becomes smaller with time. Since the PDP is a capacitive load, as discussed earlier, the CR pulse can be applied to the electrode of the PDP or the capacitance element only by supplying the voltage to the electrode through a resistance.
On the other hand, the voltage v(t) of the ramp pulse is in proportion to an application time t, and in other words, it increases (or decreases) at a constant rate of voltage change dv/dt. With the ramp pulse, unlike with the CR pulse, the discharge can be started always at a constant rate of voltage change, not depending on variation in firing voltage. Therefore, it is possible to absorb variation in discharge characteristics of the discharge cells and suppress variation in light emission all over the PDP.
(Method of Driving PDP)
Referring to a timing chart of FIG. 29, a first background-art driving method will be discussed. The timing chart of FIG. 29 is disclosed in, e.g., Japanese Patent Application Laid Open Gazette No. 10-91116.
In this driving method, one subfield is divided into four periods, i.e., a reset period, an addressing period, a sustain period and an erase period. In the reset period, all the cells are discharged or lighted, regardless of a display history, to perform a writing. Since the discharge in the reset period leads to luminescence even on a black screen display, it causes deterioration in contrast. For this reason, a CR pulse 620 is applied to the row electrodes X and Y to suppress the amount of light emission. Further, a CR pulse 620 having a negative polarity is applied to the row electrode Y and a CR pulse 620 having a positive polarity is applied to the row electrode X.
In the addressing period, a predetermined voltage is applied between the row electrode X and the column electrode W belonging to a discharge cell(s) not to be illuminated in the subsequent sustain period, to erase the wall charges in the discharge cell(s).
The above addressing method in which the wall charges are generated in all the discharge cells and then the wall charges in the discharge cell(s) not to be illuminated are erased is termed xe2x80x9can erase addressing methodxe2x80x9d. On the other hand, an addressing method in which the discharge is generated only in the discharge cell(s) to be illuminated to accumulate the wall charges is termed xe2x80x9ca write addressing methodxe2x80x9d.
In the sustain period, an AC pulse is applied to the row electrodes X and Y to generate the discharge(s) in the discharge cell(s) in which the wall charges remain because no addressing discharge is generated. This discharge illuminates the discharge cell(s). The luminance of light emission is controlled by the number of applications of the AC pulses. In the erase period, the wall charges in the discharge cell(s) illuminated in the sustain period are reduced or erased.
Next, a second background-art driving method will be discussed, referring to a timing chart of FIG. 30. The timing chart of FIG. 30 is disclosed in, e.g., U.S. Pat. No. 5,745,086.
Also in this driving method, one subfield is divided into four periods, i.e., the reset period, the addressing period, the sustain period and the erase period. Further, in the specification of the above USP, the erase period and the reset period are generally referred to as a setup period.
In the reset period, a ramp pulse or a trapezoidal pulse 610 of which voltage value changes at a constant rate of voltage change is applied to all the row electrodes X. At this time, considering that the intensity of discharge (in other words, the amount of movement of wall charges) largely depends on the rising rate of the voltage or the rate of voltage change, it is necessary to set the rate of voltage change at the rise of the ramp pulse sufficiently gentle in order to suppress the discharge or luminance of light emission.
After the wall charges are generated by the discharge at the rise of the ramp pulse 610, a voltage is applied to the row electrodes Y and the voltage applied to the row electrodes X, i.e., the ramp pulse 610 is gently lowered. At this fall, a discharge is generated to perform a full erase. At this fall, like at the rise, it is possible to suppress the luminance by setting the rate of voltage change sufficiently gentle.
In the addressing period, a scanning pulse (or address pulse) and an address data pulse are applied to the row electrodes X and the column electrode W, respectively, belonging to the discharge cell(s) to be illuminated in the subsequent sustain period, to generate an addressing discharge in the discharge cell(s) (write addressing method). In the sustain period, discharge or luminescence are generated in the discharge cell(s) in which the wall charges are accumulated by generating the addressing discharge. The luminance of light emission is controlled by the number of applications of the AC pulses.
In the erase period, a ramp pulse 611 which is sharper than the ramp pulse 610 applied in the reset period is applied to generate a discharge, thereby reducing or erasing the wall charges in the discharge cell(s) illuminated in the sustain period. It is shown in the second background-art driving method that with this operation, a stable driving voltage margin can be obtained.
Next, a third background-art driving method will be discussed, referring to a timing chart of FIG. 31. The timing chart of FIG. 31 is disclosed in, e.g., Japanese Patent Application Laid Open Gazette No. 6-289811.
In a case of using the write addressing method, first, a discharge is generated in the column electrode W and the row electrode X and then with this discharge used as a trigger, a discharge is generated between the row electrode X and the row electrode Y. With this discharge between the row electrodes X and Y, the wall charges are generated on the row electrodes X and Y.
At this time, as shown in FIG. 31, a secondary scanning pulse 650 is applied to the row electrode Y during the addressing period in the third background-art driving method. It is shown that the discharge can be reliably shifted from that between the column electrode W and the row electrode X to that between the row electrodes X and Y by forming a sufficient electric field between the row electrodes X and Y with the secondary scanning pulse 650.
Also in the second background-art driving method (see FIG. 30), a voltage almost equal to the sustain pulse is applied to the row electrode Y during the addressing period. The voltage applied during the addressing period, however, is continuously applied from the reset period with same voltage value, and such a pulse as applied thus is not exactly the secondary scanning pulse. This is because the secondary scanning pulse is a pulse to enlarge an operating margin by using an applied voltage different from that used in the reset period, in other words, by controlling the value of the applied voltage in the addressing period and that in the reset period independently of each other.
The CR pulse has the following problems. First, when the discharge is started in a time region where the rate of voltage change dv/dt is sharp immediately after application, a strong discharge is generated like in the case of using the rectangular pulse. When such a strong discharge is generated in the reset period, the luminance irrelevant to the display emission increases and this causes deterioration in contrast. Further, when the movement of the wall charges during generation of the strong discharge is too larger than the inclination of the applied waveform, the very weak discharge caused by the round pulse can not be continued. In this case, it is impossible to take full advantage of the characteristic feature of the round pulse that the amount of accumulated wall charges can be controlled by the final potential of the applied waveform. Therefore, it is necessary to design a driving sequence so that a discharge can be started in a region where the rate of voltage change dv/dt is sufficiently gentle.
Since the voltage of the ramp pulse rises at a constant inclination, even if there is variation in firing voltage among the discharge cells, it is possible to suppress this variation and obtain a sufficiently low luminance. The ramp pulse is more advantageous than the CR pulse in this point. Since the ramp pulse needs a longer time for its voltage to reach the firing voltage than the CR pulse, however, the ramp pulse sometimes needs a longer application time than the CR pulse.
The first background-art driving method has the following problems. Since the respective CR pulses 620 applied to the row electrodes X and Y in the reset period of this driving method have polarities reverse to each other, the rate of change in potential difference between the row electrodes X and Y is larger than the rate of voltage change of the CR pulse 620. Therefore, though the CR pulse 620 is applied to the row electrodes X and Y, the characteristic feature of the CR pulse can not be sufficiently obtained and for example, deterioration in contrast is liable to be caused. Further, since the first background-art driving method uses the CR pulse 620, it is disadvantageously impossible to sufficiently absorb variation in discharge characteristics among the discharge cells, unlike in the case of using the ramp pulse 610 (of FIG. 30).
The second background-art driving method has the following problem. In the reset period of this driving method, application of the ramp pulse 610 to the row electrode X is started with the potential of the row electrode Y set to the ground potential (GND). At this time, since the potential difference between the electrodes X and W is equal to that between the electrodes X and Y, a discharge is also generated between the electrodes X and W. Though very weak, this discharge disadvantageously deteriorates the phosphor 110 layer on the column electrode W.
In contrast to this, in the reset period of the first background-art driving method, since the positive CR pulse 620 is applied to the row electrode X while the negative CR pulse 620 is applied to the row electrode Y, the potential of the column electrode W becomes an intermediate potential of those of the row electrodes X and Y, and therefore it is believed that it is hard to generate any discharge in the column electrode W. Since the CR pulse 620 having a voltage high enough to generate a discharge between the row electrodes X and Y is applied, however, a discharge may be sometimes generated on the column electrode W and the phosphor layer may be deteriorated in such a case.
It is possible to generate a certain amount of wall charges by using a round pulse which gently rises (and falls), like in the first and second background-art driving methods. Since the amount of wall charges depends on the final voltage of the round pulse, however, when a plurality of round pulses are used, it is necessary to provide a plurality of round pulse generation circuits in accordance with the necessary final voltages and therefore the cost disadvantageously becomes high.
Similarly, since it is necessary to additionally provide a circuit for generating the secondary scanning pulse 650 in the third background-art driving method, the cost becomes high also in this case.
Further, since application time of the round pulse is longer than that of the rectangular pulse, when the reset period is set in all the subfields like in the first and second background-art driving method, it is necessary to reduce the sustain period and the like or reduce the number of subfields in one field. Reducing the sustain period and the like causes an unstable operation and deterioration in display quality. This problem becomes more pronounced as the number of subfields in one field increases. Furthermore, when the reset period is set in all the subfields, the luminance irrelevant to the display emission thereby disadvantageously becomes high.
Further, the background-art PDP has a problem of flicker in image caused by the longer discharge delay time in generation of the addressing discharge (or writing discharge). This problem will be discussed, referring to FIGS. 32 to 36.
First, a timing chart used for explaining a discharge delay time in the addressing period is shown in FIG. 32. FIG. 32 shows waveforms of a voltage applied to the column electrode W, a voltage applied to the row electrode X and discharge intensity. The waveform of discharge intensity can be obtained by measuring the intensity of infrared ray radiated by the discharge with a photodetector using photodiode (i.e., photoprobe).
As shown in FIG. 32, in the addressing period, the addressing discharge starts behind the point of time when the application of an address pulse Pa and a data pulse Pd starts by a discharge delay time xcfx84d. For this reason, to ensure the writing operation, it is necessary to apply the address pulse Pa and the data pulse Pd until the discharge grows to accumulate wall charges also after the addressing discharge starts. In other words, to ensure the writing operation, the discharge delay time xcfx84d has to be not longer than a predetermined time period (hereinafter referred to also as xe2x80x9caddress limit time widthxe2x80x9d) xcfx84th (see FIG. 34 discussed below) which is shorter than the pulse width (hereinafter referred to also as xe2x80x9caddressing time widthxe2x80x9d) xcfx84w of the address pulse Pa and the data pulse Pd.
The discharge delay time xcfx84d is not constant, probabilistically changing. Therefore, when the discharge delay time xcfx84d is almost equal to the address limit time width xcfx84th or longer, the addressing discharge is not probabilistically generated in some cases. In such a case, a discharge cell which should be lighted is not lighted (in a case of write addressing method) or a discharge cell which should not be lighted is wrongly lighted (in a case of erase addressing method) in the sustain period. As a result, problems such as flicker in image arise.
The probability distribution of the discharge delay time xcfx84d depends on the content of the display image. This will be discussed, referring to FIGS. 33 to 36. FIGS. 33 and 35 are schematic views of PDPs, used for explaining a full lighting display and a solitary lighting display, respectively, and FIGS. 34 and 36 are schematic views used for explaining probability distribution of the discharge delay time xcfx84d in the full lighting display and the solitary lighting display, respectively. Further, in FIGS. 33 and 35, a lighting discharge cell C is represented by solid circle (xe2x97xaf) and a not-lighting discharge cell C is represented by blank circle (∘).
The full lighting display refers to a state where all the discharge cells C arranged in matrix are lighted as shown in FIG. 33. On the other hand, the solitary lighting display refers to a state where the lighting discharge cells C are scattered and the discharge cells C surrounding the lighting discharge cell C are not lighted as shown in FIG. 35.
As shown in FIG. 34, when the content of the display image is the full lighting display, the discharge delay time xcfx84d is shorter than the addressing time width xcfx84w and the address limit time width xcfx84th, and its distribution falls in a narrow time range. On the other hand, as shown in FIG. 36, when the content of the display image is the solitary lighting display, the distribution of the discharge delay time xcfx84d is wide (varies) and extends beyond the addressing time width xcfx84w and the address limit time width xcfx84th in a wide time range. In this case, when the discharge delay time xcfx84d exceeds the address limit time width xcfx84th, no addressing discharge is generated.
The reason for the difference of distribution between FIGS. 34 and 36 is considered as follows. In the case of the full lighting display, when the addressing discharge is generated in a discharge cell, the priming particles generated by the addressing discharge are diffused to the discharge cells therearound and a priming effect is produced in the discharge cell in which the addressing discharge is generated next. In contrast to this, in the case of solitary lighting display, there is no source for priming particles around the discharge cell in which the addressing discharge is generated. This is considered to produce the above difference in the distribution of the discharge delay time xcfx84d.
As discussed above, the distribution of the discharge delay time xcfx84d extends beyond the addressing time width xcfx84w and the address limit time width xcfx84th in a wide range (see FIG. 36). Therefore, some lighting problem is more likely to arise in the solitary lighting display than in the full lighting display. In this case, it is considered that writing probability is raised (a) by widening the pulse width of the address pulse Pa (in other words, by making the addressing time width xcfx84w longer), or (b) by raising the voltage of the address pulse Pa (address voltage), to reduce the flicker. Further, the writing probability refers to a probability of completing the writing operation within the address limit time width xcfx84th, in other words, a probability that the discharge delay time rd is shorter than the address limit time width xcfx84th.
When the pulse width of the address pulse Pa is widened (a), however, since the addressing period becomes longer, the ratio of the addressing period in one subfield becomes larger. As a result, for example, the sustain period has to be shorten, and another problem such as deterioration in luminance arises. On the other hand, when the voltage of the address pulse Pa is raised (b), an address driving device of high breakdown voltage is needed, and the cost for the driving device is disadvantageously raised.
Japanese Patent Application Laid Open Gazette No. 10-91116, as shown in FIG. 29, discloses a driving method in which an operation for generating a priming discharge by applying a priming pulse 623 before the application of an address pulse 622 by a predetermined time is performed for each row. In the driving method, since the priming particles are generated immediately before the addressing operation, the flicker in image is relatively unlikely to occur even in the case of solitary lighting display.
In the driving method of FIG. 29, however, since the address pulse 622 and the priming pulse 623 are sequentially applied for each row, the waveform of application voltage is complicated and accordingly the driving device becomes complicated. As a result, the cost is disadvantageously raised. Further, the luminescence by the priming discharge is observed as background luminescence, in other words, luminescence in black display, and therefore there arises a problem that the contrast can not become so high.
The present invention is directed to a method of driving a plasma display panel which comprises a discharge cell including a first electrode and a second electrode, capable of controlling generation/non-generation of discharge with potential difference between the first electrode and the second electrode.
(1) According to a first aspect of the present invention, in the method of driving a plasma display panel, a pulse generation system for generating a voltage pulse which continuously changes from a first voltage to a second voltage is prepared, and application of the voltage pulse to the first electrode is started by using the pulse generation system, and then the change of the voltage pulse is stopped at the point of time when the voltage pulse reaches a third voltage between the first voltage and the second voltage.
(2) According to a second aspect of the present invention, in the method of the first aspect, the third voltage is set on the side of the second voltage relative to a firing voltage, and the voltage pulse reaches the third voltage after a time longer than a discharge delay time passes from the point of time when the voltage pulse exceeds the firing voltage.
(3) According to a third aspect of the present invention, in the method of the first or second aspect, the voltage pulse includes at least one of a CR voltage pulse, a ramp voltage pulse and an LC resonant voltage pulse.
(4) According to a fourth aspect of the present invention, in the method of the third aspect, a rectangular pulse generation system for generating a rectangular voltage pulse is further prepared, and a voltage pulse in which one of the CR voltage pulse, the ramp voltage pulse and the LC resonant voltage pulse is superimposed on the rectangular voltage pulse is applied between the first electrode and the second electrode by using the pulse generation system and the rectangular pulse generation system.
(5) According to a fifth aspect of the present invention, in the method of any one of the first to fourth aspects, when one field for image display is divided into a plurality of subfields each including an addressing period and a sustain period set after the addressing period, whether the discharge cell should be illuminated or not in the sustain period is determined in the addressing period and the discharge cell is illuminated in the sustain period if it is determined in the addressing period that the discharge cell should be illuminated, application of the voltage pulse is started and stopped in a period other than the addressing period and the sustain period in at least one of the subfields in the one field.
(6) According to a sixth aspect of the present invention, in the method of the fifth aspect, at least one of an operation for generating a discharge in the discharge cell regardless of a display history and an operation for generating a discharge in the discharge cell only when the discharge cell is illuminated in the immediately preceding sustain period is performed with the voltage pulse.
(7) According to a seventh aspect of the present invention, in the method of the fifth or sixth aspect, application of the voltage pulse to the first electrode is started before the addressing period, and the third voltage of the voltage pulse is set to a value between a ground potential and an address voltage to be applied to the first electrode in the addressing period in determining that the discharge cell should be illuminated in the sustain period.
(8) According to an eighth aspect of the present invention, in the method of driving a plasma display panel, one field for image display is divided into a plurality of subfields each including an addressing period and a sustain period set after the addressing period, an address voltage is applied to the first electrode and whether the discharge cell should be illuminated or not in the sustain period is determined in the addressing period, and the discharge cell is illuminated in the sustain period when it is determined in the addressing period that the discharge cell should be illuminated. The method comprises the steps of: (a) applying a first voltage pulse having the same polarity as the address voltage has to the first electrode for generating a discharge to generate wall charges in the discharge cell; and (b) applying a second voltage pulse having the same polarity as the first voltage pulse has to the first electrode for generating a discharge to control the state of the wall charges, and in the method of the eighth aspect, both the steps (a) and (b) are performed before the addressing period and the step (b) is performed after the step (a), and the first voltage pulse and the second voltage pulse have waveforms of which absolute values continuously increase toward a predetermined polarity.
(9) According to a ninth aspect of the present invention, the method of the eighth aspect further comprises the step of: (c) applying a third voltage pulse having a polarity reverse to that of the first voltage pulse to the first electrode, and in the method of the ninth aspect, the step (c) is performed between the step (a) and the step (b), and the third voltage pulse has a waveform of which absolute value continuously increases toward a predetermined polarity.
(10) According to a tenth aspect of the present invention, the method of the eighth or ninth aspect further comprises the step of: (d) reducing the wall charges in the discharge cell, and in the method of the tenth aspect, the step (d) is performed before the step (a).
(11) According to an eleventh aspect of the present invention, in the method of the tenth aspect, the step (d) comprises the steps of: (d-1) applying a fourth voltage pulse between the first electrode and the second electrode to generate a discharge in the discharge cell; and (d-2) applying a fifth voltage pulse between the first electrode and the second electrode to generate a discharge in the discharge cell, and in the method of the eleventh aspect, the step (d-1) and the step (d-2) are sequentially performed, the fourth voltage pulse is a voltage pulse which is capable of generating a discharge at the rise and the fall of the fourth voltage pulse, and the fifth voltage pulse has a waveform of which absolute value continuously increases toward a predetermined polarity.
(12) According to a twelfth aspect of the present invention, the present invention is directed to the method of driving a plasma display panel which comprises a discharge cell including a first electrode and a second electrode, capable of controlling generation/non-generation of discharge with potential difference between the first electrode and the second electrode, and in the method of driving a plasma display panel, a discharge is sequentially generated in the discharge cell by sequentially applying two voltage pulses between the first electrode and the second electrode, a latter voltage pulse which is applied later among the two voltage pulses changes more gently than a former voltage pulse which is applied first among the two voltage pulses, and the latter voltage pulse is applied in a period while priming particles generated in the discharge by the former voltage pulse remain in the discharge cell.
(13) According to a thirteenth aspect of the present invention, in the method of driving a plasma display panel, the discharge is generated in the discharge cell during an 110 operation for defining whether the discharge cell is illuminated for display or not, regardless of whether the discharge cell is illuminated for display or not.
(14) According to a fourteenth aspect of the present invention, in the method of driving a plasma display panel of the thirteenth aspect, the plasma display panel comprises a plurality of the discharge cells, and the discharge includes a first discharge and a second discharge weaker than the first discharge, the method of driving a plasma display panel includes the operations, as the operation for defining whether the discharge cell is illuminated for display or not, of: sequentially applying an address pulse to the first electrode of each of the plurality of discharge cells to sequentially select the plurality of discharge cells, generating the first discharge in a selected one of the plurality of discharge cells when a data pulse is applied to the second electrode of the selected discharge cell, and generating the second discharge in the selected discharge cell when the data pulse is not applied to the second electrode of the selected discharge cell.
(15) According to a fifteenth aspect of the present invention, in the method of driving a plasma display panel of the thirteenth or fourteenth aspect, a pulse generation system for generating a voltage pulse which continuously changes from a first voltage to a second voltage is prepared, and application of the voltage pulse to the first electrode is started by using the pulse generation system, then the change of the voltage pulse is stopped at the point of time when the voltage pulse reaches a third voltage between the first voltage and the second voltage, and thereafter the operation for defining whether the discharge cell is illuminated for display or not is performed.
The present invention is also directed to a plasma display device.
(16) According to a sixteenth aspect of the present invention, the plasma display device comprises a plasma display panel comprising a discharge cell including a first electrode and a second electrode; and a driving unit for driving the discharge cell by giving a potential difference between the first electrode and the second electrode, and in the plasma display device of the twelfth aspect, the driving unit comprises a pulse generation unit capable of generating a voltage pulse which continuously changes from a first voltage to a second voltage, and the driving unit controls the pulse generation unit to start outputting the voltage pulse as a voltage to be applied to the first electrode and then to stop the change of the voltage pulse at the point of time when the voltage pulse reaches a third voltage between the first voltage and the second voltage.
(17) According to a seventeenth aspect of the present invention, in the plasma display device of the sixteenth aspect, the third voltage is set on the side of the second voltage relative to a firing voltage, and the voltage pulse reaches the third voltage after a time longer than a discharge delay time passes from the point of time when the voltage pulse exceeds the firing voltage.
(18) According to an eighteenth aspect of the present invention, in the plasma display device of the sixteenth or seventeenth aspect, the voltage pulse includes at least one of a CR voltage pulse, a ramp voltage pulse and an LC resonant voltage pulse.
(19) According to a nineteenth aspect of the present invention, in the plasma display device of the eighteenth aspect, the pulse generation unit is capable of generating a rectangular voltage pulse, and the driving unit controls the pulse generation unit to output a voltage pulse in which one of the CR voltage pulse, the ramp voltage pulse and the LC resonant voltage pulse is superimposed on the rectangular voltage pulse, as a voltage to be applied between the first electrode and the second electrode.
(20) According to a twentieth aspect of the present invention, in the plasma display device of any one of the sixteenth to nineteenth aspects, when one field for image display is divided into a plurality of subfields each including an addressing period and a sustain period set after the addressing period, whether the discharge cell should be illuminated or not in the sustain period is determined in the addressing period and the discharge cell is illuminated in the sustain period if it is determined in the addressing period that the discharge cell should be illuminated, the driving unit starts and stops applying the voltage pulse in a period other than the addressing period and the sustain period in at least one of the subfields in the one field.
(21) According to a twenty-first aspect of the present invention, in the plasma display device of the twentieth aspect, the driving unit performs, with the voltage pulse, at least one of an operation for generating a discharge in the discharge cell regardless of a display history and an operation for generating a discharge in the discharge cell only when the discharge cell is illuminated in the immediately preceding sustain period.
(22) According to a twenty-second aspect of the present invention, in the plasma display device of the twentieth or twenty-first aspect, the driving unit starts outputting the voltage pulse as a voltage to be applied to the first electrode before the addressing period, and the third voltage of the voltage pulse is set to a value between a ground potential and an address voltage applied to the first electrode in the addressing period in determining that the discharge cell should be illuminated in the sustain period.
(23) According to a twenty-third aspect of the present invention, the plasma display device comprises a plasma display panel comprising a discharge cell including a first electrode and a second electrode; and a driving unit for driving the discharge cell by giving a potential difference between the first electrode and the second electrode, and in the plasma display device of the nineteenth aspect, one field for image display is divided into a plurality of subfields each including an addressing period and a sustain period set after the addressing period, an address voltage is applied to the first electrode and whether the discharge cell should be illuminated or not in the sustain period is determined in the addressing period, and the discharge cell is illuminated in the sustain period when it is determined in the addressing period that the discharge cell should be illuminated. Further, in the plasma display panel of the nineteenth aspect, the driving unit performs the steps of: (a) generating a first voltage pulse having the same polarity as the address voltage has, for generating a discharge in the discharge cell to generate wall charges, and outputting the first voltage pulse as a voltage to be applied to the first electrode; and (b) generating a second voltage pulse having the same polarity as the first voltage pulse has, for generating a discharge in the discharge cell to control the state of the wall charges, and outputting the second voltage pulse as a voltage to be applied to the first electrode, both the steps (a) and (b) are performed before the addressing period and the step (b) is performed after the step (a), and the first voltage pulse and the second voltage pulse have waveforms of which absolute values continuously increase toward a predetermined polarity.
(24) According to a twenty-fourth aspect of the present invention, in the plasma display device of the twenty-third aspect, the driving unit further performs the step of: (c) generating a third voltage pulse having a polarity reverse to that of the first voltage pulse and outputting the third voltage pulse as a voltage to be applied to the first electrode, the step (c) is performed between the step (a) and the step (b), and the third voltage pulse has a waveform of which absolute value continuously increases toward a predetermined polarity.
(25) According to a twenty-fifth aspect of the present invention, in the plasma display device of the twenty-third or twenty-fourth aspect, the driving unit further performs the step of: (d) reducing the wall charges in the discharge cell, and the step (d) is performed before the step (a).
(26) According to a twenty-sixth aspect of the present invention, in the plasma display device of the twenty-fifth aspect, the driving unit sequentially performs, in the step (d), the steps of: (d-1) generating a fourth voltage pulse for generating a discharge in the discharge cell and outputting the fourth voltage pulse as a voltage to be applied between the first electrode and the second electrode; and (d-2) generating a fifth voltage pulse for generating a discharge in the discharge cell and outputting the fifth voltage pulse as a voltage to be applied between the first electrode and the second electrode, the fourth voltage pulse is a voltage pulse which is capable of generating a discharge at the rise and the fall of the fourth voltage pulse, and the fifth voltage pulse has a waveform of which absolute value continuously increases toward a predetermined polarity.
(27) According to a twenty-seventh aspect of the present invention, the plasma display device comprises a plasma display panel comprising a discharge cell including a first electrode and a second electrode; and a driving unit for driving the discharge cell by giving a potential difference between the first electrode and the second electrode, and in the plasma display device of the twenty-seventh aspect, the driving unit sequentially applies two voltage pulses between the first electrode and the second electrode to sequentially generate a discharge in the discharge cell, a latter voltage pulse which is applied later among the two voltage pulses changes more gently than a former voltage pulse which is applied first among the two voltage pulses, and the driving unit applies the latter voltage pulse in a period while priming particles generated in the discharge by the former voltage pulse remain in the discharge cell.
(28) According to a twenty-eighth aspect of the present invention, the plasma display device comprises a plasma display panel comprising a discharge cell including a first electrode and a second electrode; and a driving unit for driving the discharge cell by giving a potential difference between the first electrode and the second electrode, and in the plasma display device of the twenty-eighth aspect, the driving unit generates the discharge in the discharge cell during an operation for defining whether the discharge cell is illuminated for display or not, regardless of whether the discharge cell is illuminated for display or not.
(29) According to a twenty-ninth aspect of the present invention, in the plasma display device of the twenty-eighth aspect, the plasma display panel comprises a plurality of the discharge cells, and the discharge includes a first discharge and a second discharge weaker than the first discharge, the driving unit performs the operations, as the operation for defining whether the discharge cell is illuminated for display or not, of: sequentially applying an address pulse to the first electrode of each of the plurality of discharge cells to sequentially select the plurality of discharge cells, generating the first discharge in a selected one of the plurality of discharge cells when a data pulse is applied to the second electrode of the selected discharge cell, and generating the second discharge in the selected discharge cell when the data pulse is not applied to the second electrode of the selected discharge cell.
(30) According to a thirtieth aspect of the present invention, in the plasma display device of the twenty-eighth or twenty-ninth aspect, the driving unit comprises a pulse generation unit capable of generating a voltage pulse which continuously changes from a first voltage to a second voltage, and the driving unit controls the pulse generation unit to start outputting the voltage pulse as a voltage to be applied to the first electrode, then to stop the change of the voltage pulse at the point of time when the voltage pulse reaches a third voltage between the first voltage and the second voltage and thereafter to perform the operation for defining whether the discharge cell is illuminated for display or not.
The present invention is further directed to a driving device for a plasma display panel.
(31) According to a thirty-first aspect of the present invention, the driving device for a plasma display panel comprising a discharge cell including a first electrode and a second electrode comprises the driving unit as defined in any one of the sixteenth to thirtieth aspects.
(1) In the method of the first aspect of the present invention, by setting the third voltage to various values, it is possible to easily generate a plurality of kinds of voltage pulses by one pulse generation system and apply the voltage pulses to the first electrode. This ensures reduction in cost of the plasma display device.
(2) By the method of the second aspect of the present invention, a continuous very weak discharge can be generated with the voltage pulse. Therefore, by generating the discharge irrelevant to the display emission with the voltage pulse, it is possible to improve the contrast as compared with, e.g., a case of using a rectangular voltage pulse. Further, an effect caused by the continuous very weak discharge, such as a stable generation of a constant amount of wall charges which depend on the voltage at the end of application of the voltage pulse, can be obtained and this stabilizes a (display) operation.
(3) The method of the third aspect of the present invention can produce the same effects as the method of the first or second aspect produces.
(4) By the method of the fourth aspect of the present invention, it is possible to reduce a change time by the voltage of the rectangular voltage pulse.
(5) In the method of the fifth aspect of the present invention, the application of the voltage pulse is started and stopped in a period other than the addressing period and the sustain period. Therefore, it is possible to reduce the time irrelevant to the display, such as the reset period and the erase period. Since there arises a time margin in one field by the reduction of time, by utilizing the time margin for an increase in the number of sustain pulses or subfields and the like, the luminance of light emission and the number of tones can be increased. Further, by generating the continuous very weak discharge with the voltage pulse, the discharge irrelevant to the display emission in the reset period and the like can be weaken and the contrast can be thereby improved. With these effects, the display quality can be improved.
(6) The method of the sixth aspect of the present invention can produce the same effect as the method of the fifth aspect produces. At this time, when e.g., the operation of generating a discharge in a discharge cell regardless of the display history is not performed in at least one subfield of one field, a time margin thereby arises in one field. Therefore, by utilizing the time margin for an increase in the number of sustain pulses or subfields and the like, the luminance of light emission and the number of tones can be increased to improve the display quality.
(7) By the method of the seventh aspect of the present invention, it is possible to optimize the amount of wall charges at the start of the addressing period. Further, by setting the third voltage equal to the address voltage, one circuit can be used both for generating the third voltage and for generating the address voltage and this ensures reduction in cost of the plasma display device. Furthermore, by setting the third voltage to a voltage which is obtained by subtracting the voltage of the secondary scanning pulse from the address voltage, it becomes possible to achieve the action of the secondary scanning pulse without applying the secondary scanning pulse to the second electrode in the addressing period. At this time, since no circuit for generating the secondary scanning pulse is needed, the cost of the plasma display device can be thereby reduced.
(8) By the method of the eighth aspect of the present invention, it is possible to control the state of the wall charges in the step (b) before the addressing period. Therefore, the state of the wall charges at the start of the addressing period can be optimized. Further, when the plasma display panel has a plurality of discharge cells, it is possible to suppress an abnormal discharge between adjacent discharge cells. As a result, the operations of the addressing period and the sustain period can be reliably performed and a (display) operation can be stabilized. Furthermore, since the first voltage pulse and the second voltage pulse have waveforms of which absolute values continuously increase toward a predetermined polarity, an unnecessary luminescence can be suppressed to improve the contrast as compared with the case of using the rectangular voltage pulse.
(9) By the method of the ninth aspect of the present invention, it is possible to more reliably control the state of wall charges in the step (b). Therefore, the effect of the method of the eighth aspect can be produced more pronouncedly. Further, since the respective polarities of the first to third voltage pulses alternately change, the voltage to be applied to the first electrode becomes smaller than in the case where all the first to third voltage pulses have, e.g., positive polarity. Therefore, it is possible to suppress deterioration of the phosphor layer provided in the discharge cell.
(10) In the method of the tenth aspect of the present invention, since the state of the wall charges can be uniformized regardless of the display history, it is possible to more reliably generate the wall charges in the step (a).
(11) In the method of the eleventh aspect of the present invention, the wall charges are reduced in two steps by applying the fourth voltage pulse first and subsequently applying the fifth voltage pulse. Therefore, it is possible to reduce the wall charges better than in the case of using only the fourth voltage pulse. At this time, when the plasma display panel has a plurality of discharge cells, the state of the wall charges among the plurality of discharge cells after the step (d) can be uniformized. As a result, the effect of the method of the tenth aspect can be obtained all over the plasma display panel.
(12) In the method of the twelfth aspect of the present invention, since the latter voltage pulse is applied in the period while the priming particles generated in the discharge by the former voltage pulse remain in the discharge cell, it is possible to smoothly start the discharge by the latter voltage pulse (including the very weak continuous discharge discussed below). As a result, the driving voltage margin can be enlarged. Further, the designing flexibility of the latter voltage can be enhanced when the very weak continuous discharge is generated by the latter voltage.
(13) In the method of the thirteenth aspect of the present invention, using the priming particles by the discharge in one discharge cell, the discharge in the other discharge cell can be generated more reliably. Therefore, as compared with a case where only the discharge for illuminating the discharge cell for display, for example, is generated, the above discharge for illuminating the discharge cell for display can be generated more reliably. As a result, the operation for defining whether the discharge cell is illuminated for display or not is stabilized and an image of high quality in which flicker or the like is suppressed can be obtained.
(14) In the method of the fourteenth aspect of the present invention, the discharge (the first discharge or the second discharge) is generated in the selected discharge cell, regardless of whether the data pulse is applied to the second electrode or not. In this case, since a plurality of discharge cells are sequentially selected, by using the priming particles generated by the first discharge or the second discharge in the discharge cell selected before, the first discharge or the second discharge in the discharge cell selected next can be generated more reliably. As a result, as compared with a case where the second discharge is not generated, the first discharge can be generated more reliably in the whole plasma display panel and the effect of the thirteenth aspect can be produced.
(15) In the method of the fifteenth aspect of the present invention, by setting the third voltage, the discharge can be generated in the discharge cell during the operation for defining whether the discharge cell is illuminated for display or not, regardless of whether the discharge cell is illuminated for display or not. As a result, the effects of the thirteenth or fourteenth aspect can be reliably produced.
(16) The plasma display device of the sixteenth aspect of the present invention can produce the same effect as the method of the first aspect produces.
(17) The plasma display device of the seventeenth aspect of the present invention can produce the same effect as the method of the second aspect produces.
(18) The plasma display device of the eighteenth aspect of the present invention can produce the same effect as the method of the third aspect produces.
(19) The plasma display device of the nineteenth aspect of the present invention can produce the same effect as the method of the fourth aspect produces.
(20) The plasma display device of the twentieth aspect of the present invention can produce the same effect as the method of the fifth aspect produces.
(21) The plasma display device of the twenty-first aspect of the present invention can produce the same effect as the method of the sixth aspect produces.
(22) The plasma display device of the twenty-second aspect of the present invention can produce the same effect as the method of the seventh aspect produces.
(23) The plasma display device of the twenty-third aspect of the present invention can produce the same effect as the method of the eighth aspect produces.
(24) The plasma display device of the twenty-fourth aspect of the present invention can produce the same effect as the method of the ninth aspect produces.
(25) The plasma display device of the twenty-fifth aspect of the present invention can produce the same effect as the method of the tenth aspect produces.
(26) The plasma display device of the twenty-sixth aspect of the present invention can produce the same effect as the method of the eleventh aspect produces.
(27) The plasma display device of the twenty-seventh aspect of the present invention can produce the same effect as the method of the twelfth aspect produces.
(28) The plasma display device of the twenty-eighth aspect of the present invention can produce the same effect as the method of the thirteenth aspect produces.
(29) The plasma display device of the twenty-ninth aspect of the present invention can produce the same effect as the method of the fourteenth aspect produces.
(30) The plasma display device of the thirtieth aspect of the present invention can produce the same effect as the method of the fifteenth aspect produces.
(31) By the driving device of the thirty-first aspect of the present invention, it is possible to provide an driving device for plasma display panel which can produce any one of the effects of the sixteenth to thirtieth aspects.
A first object of the present invention is to provide a method of driving a plasma display panel, which makes it possible to generate a plurality of kinds of voltage pulses by using one pulse generation system.
A second object of the present invention is to provide a method of driving a plasma display panel, which ensures stabilization of a (display) operation and/or improvement in display quality, as well as achieves the first object.
A third object of the present invention is to provide a method of driving a plasma display panel, which achieves the first and second objects at low cost.
A fourth object of the present invention is to provide a plasma display device and a driving device for plasma display panel which achieve the first to third objects.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.